Impact of Hijlan Creek springs on water quality of the Euphrates River and the hydrochemical characterization of the contamination plumes

The aim of this work is to present the hydrochemical mechanisms describing the system of the Euphrates River before and after mixing with groundwater from the springs of Hijlan (western Iraq). Continuously, the data generated from these springs water have been adapted to provide an updated assessment for future water therapeutic purposes. Physicochemical characteristics of water in the mixing plume of Hijlan Creek and Euphrates indicate the multi Hydrochemical plumes as revealed by the spatial variation of important parameters related to the ecological parameters including K+, Na+, Ca2+, Mg2+, HCO3−, SO42−, Cl−, NO3−, PO43−, Pb, Zn, Cd, Fe, Mn, Temp, DO, BOD5, H2S, Turbidity, EC, pH, and TDS. The re-aeration (k2) and de-oxygenation rate (k1) coefficients, as well as the self-purification factor (f) of the mixing plume, are 0.51, 2.03 and 0.25 s−1, respectively. The Cl− concentration in the confluence zone changes, due to the chloride content mixing rates of 7.1 and 92.9% for Euphrates and Hijlan creek water, respectively, with water discharge of 316,224 m3/day and chloride load discharge of 420 tons/day. The assessment of the water quality indicates unsuitability for aquaculture purposes. However, the water can be used for therapeutic purposes and to cure multiple diseases.


Introduction
Environmental concerns are growing with variations in water resource pollutants. Numerous rivers are vulnerable to disasters due to the increase of pollutants (Gurnell et al. 2020;Rabeea et al. 2020). River water has traditionally been seen as a disposal site for waste coming from a variety of activities, believing that a large amount of water by dilution leads to detoxification (Nguyen et al. 2020;Vandana et al. 2020). Contamination of the rivers is one of the greatest challenges facing the new world, which is creating an unsettling situation. Increased human activities and natural resources (groundwater and spring water) flowing into rivers make it necessary to evaluate the current water quality of rivers and predict potential improvements (Gao et al. 2019;Fregoso-López et al. 2020). The water quality indexes may be divided into specified indicators, public indicators, planning and designing indicators, and statistical indicators. Statistical models are significantly important when they are used to evaluate water quality (Marta et al. 2010;Jena et al. 2013;Cruz et al. 2019 The surface and groundwater resources of the study area have been covered by several previous reports (Fayadh et al. 2016;Hussein et al. 2020;Hussein et al. 2021). Techno promo export (1978) studied the groundwater and surface water resources in the study area, which was the basis for establishing Haditha Dam . Consortium Yugoslavia (1981) performed hydrogeological tests to explore the water resources within block 7 in the Western Desert. Al- Hadithi (1994) studied the hydrology of Haditha reservoir and pointed out the contribution of Haditha lake and groundwater recharge. Al Jabbari et al. (2002) studied Euphrates basin within the national monitoring program, which includes the groundwater adjacent to the Euphrates River. Hussein (2010) utilized the intersection of groundwater with surface water to describe the movement and levels of the groundwater along the Euphrates River in Al-Anbar province. A statistical study of the source and origin of the hydro-chemical constituents in the Euphrates River from Al-Qa'im District to Al-Baghdadi city was conducted via government observation during water surplus and deficit periods in 2007 (Al Hamdany et al. 2012).
The Euphrates River has been exposed to decades-old hazards of contamination from continuous groundwater discharge as flowing springs (Hijlan springs) dispose into the river. A feasible program of field monitoring was conducted to obtain the ambient water quality data in the mixing zone of Euphrates, which was formed in a restricted confluence region due to Hijlan creek discharge. The Creek water behaves as a plume of point source or minero-medicinal water but can be considered a point source of pollution due to the inflow of salt additives, ions, and other elements into the Euphrates. Therefore, it is necessary to assess the degradation degree of the river contamination in the confluence zone. This study is an attempt to determine the characteristics of the Euphrates River water before and after mixing with Hijlan springs creek (statistical and spatial evaluation). We also investigate the amount of total load added to the Euphrates and the mixing case using the chloride concentration. Continuously, the variation of the concentration of chemical components within the deterioration plume, the aeration phenomenon using the dissolved oxygen concentration, the possibility of using spring mineral water for therapeutic purposes, recreation after improvement, and environmental regulation of the Hijlan Creek are investigated.

Study area
Hijlan Springs are found in the confluence region of Hijlan Creek with Euphrates River, locating at a distance of approximately 3 km north of Haqlaniyah town, Haditha provinces, Al-Anbar Governorate, bounded by UTM Northing of 255,000 to 260,000 and Easting of 3,773,000 and 3,777,000, (Fig. 1). The mean annual temperatures, rainfall, evapotranspiration during  of Hijlan Springs were 21.9 °C, 138.9, and 3088 mm, respectively. The climate in the study area is arid based on the classification of Mather (1974). Positive AI values indicate a humid climate, while negative values indicate a dry climate.
Geologically the area covered by sedimentary rocks is aged from the late Oligocene to Early Miocene (Sissakian and Hafidh 1994), represented by the Anah and Euphrates Formations that are exposed near to Haqlaniyah town in the deep cutting of Hijlan valley. Anah Formation (Upper Oligocene) is composed mainly massively bedded and hard dolomitic limestone and cavernous limestone, which are locally strongly Karastified resulting in the composition of differently sized cavities (Sissakian and AL-Mousawi 2007). The exposed formation has an approximate thickness of 6-10 m. The Anah formation is overlain unconformably by the Euphrates formation (Lower Miocene), which is composed of the early Miocene sediments. Euphrates formation is exposed along both banks of the Euphrates River.
The formation changes in both horizontal and vertical directions. It consists of two members. Lower Member consists of basal conglomerate, which plays a big role in water circulation and development of the sinkholes. The conglomerate is overlain by well-bedded and hard dolomitic limestone, dolomite, and limestone; followed by thickly bedded chalky limestone; upwards become thinly bedded. This succession forms all the flat areas and all the sinkholes are developed in the succession (Mahdi et al. 1985;Aljahdali et al. 2020), with a thickness range of 5-25 m. The upper member consists of brecciated and highly deformed limestone, dolostones, and dolomitic limestone with horizons and lenses of green mud, and a thickness range of 7-15 m (Fig. 1). These Formations are covered by residual soil and/ or alluvial soil (Gypsious and Calcareous soils). Karst phenomenon including landforms, Sinkholes karst types, caves are the most common karst forms in the study area. Surface karstification is manifested as numerous sinkholes and shallow holes of regular shapes and vertical wells depressions (Abdul Razzak and Zaynal 2012).
The Euphrates River incises its course through the Miocene and Oligocene sediments in the sight of Wadi Hijlan springs between Haditha and al-Baghdadi sections CC1 and DD1 (Fig. 2). The Euphrates and Anah Formations are considered as the major aquifers with semi-confined conditions and their water flow towards the discharge zone as springs. It is important to note that the water-bearing horizons of the Quaternary sediments are characterized by bank storage conditions and serve as a control in the relationship between the groundwater of aquifers and the surface waters of the Euphrates.

Study site description and sampling
The equipment used in the hydrographic survey is Trimble Global Positioning System AG122 (GPS), Surfer software, and field notebook computer. GPS is used to determine exact locations (XY coordinates) on earth's surface with approximately five to seven satellites locked in on the receiver at one time to ensure the highest level of accuracy. Surfer Software was used to map the positions of the survey grids (UTMzone-38) within the study area and during boat travels across the river surface. Thirty-five points were fixed for the sampling of water and the various measurements. Data collection was performed in November 2019. Data generated from the monitoring procedure were used to produce an updated view of Hijlan Springs Creek. A total of 286 different readings were recorded during the monitoring period (Tables S1-S2 in supplementary file).
Five water samples (S1, R1, M1, R2, and R3) were collected from Hijlan Creek and Euphrates (Fig. 3) for the analysis of major cations, anions, minor anions, and trace elements. Six sites (H1, H2, H3, H4, H5, and H6) in the Hijlan (Table S1 in supplementary file) Creek were identified for the field analysis. Continuously, twenty-four field measurements numbered (D1-D24) have been monitored along 250 m at the confluence of Hijlan Creek and Euphrates to meet the research objectives (Table S2 in supplementary  file).
Water samples were collected using polyethylene bottles according to the procedures of USEPA (2000). The samples were carefully sealed and tagged. The equipment used for sample collection was cleaned using deionized water (Barcelona et al. 1985;Shelton 1994).

Physico-chemical and heavy metal analysis
The collected samples were transferred to a quality control laboratory to analyze for all ions (K + , Na + , Ca 2+ , Mg 2+ , HCO 3− , SO 4 2− , Cl − , NO 3− and PO 4 3− ), using the standard methods of the American Public Health Association (APHA, AWWA, WEF 1995; APHA 2012). Trace elements (Pb, Zn, Cd, Fe, and Mn) were determined using Flame Cont. AA-7000 SHIMADZU (ROM Version, 1.03, S/N, A30945100295). The field analysis (Temperature, pH, EC, TDS, and DO) were achieved using a portable multi-digit device (Aquaread AP-800-P). The H 2 S dissolved in Hijlan Creek was determined by the addition of lead acetate to precipitate as lead sulfide for analysis. Turbidity values were expressed as nephelometric turbidity units (NTU) using a HACH 2100P field turbid-meter. The rank correlation coefficient of Spearman was used to determine the degree of importance and the value of the relationship between studied variables (Helsel and Hirsch 2002;Allam et al. 2020).

Self-purification factor
The model of space-time evolution of the concentration of dissolved oxygen (DO) and biological oxygen demand (BOD 5 ) towards downstream after contaminated discharges (Streeter and Phelps 1925), was described as: where: D t denotes dissolved oxygen deficit, C s represents saturated DO concentration (mg/l), and C stands for concentration of DO detected in DO plume.

Contaminants loads
The discharge is directly calculated from the velocity and cross-sectional area of the Creek using the formula (3): where: Q is the discharge flowrate [L 3 /t] m 3 /s; V is the average flow velocity (L/T) m/s; A is the cross-sectional area of the portion of the channel occupied by the flow (L 2 ) m 2 . Calculating the discharge is crucial for the prediction of contaminant transport and load. Using the HOL procedure (Brikowski 2011), an Impeller flow meter was utilized to determine average velocity across the entire Creek (Hijlan estuary) and right bank of the Euphrates river. The morphometric feature, velocity, and water discharge results are listed in Tables 1 and 2.

Contamination plume behavior and characterization
A statistical comparison of the concentrations of ions versus total dissolved solids and the physicochemical components where d i = x i − y i represents the difference in ranks for the i-th individual and n denotes the number of individuals (Helsel and Hirsch 2002).
Positive associations of ranks are observed between TDS and H 2 S for all parameters, except for Co and Mn (Table 3) due to the impact of H 2 S on their concentration via precipitation mechanism. Both Co and Mn are confirmed by a linear positive relationship to the DO concentration. The emergence of a close correlation between the measured physicochemical variables is a contamination indicator and it trends the active effect of the spring water on surface water.

PH, dissolved oxygen, biological oxygen demand, and nitrate plume
Physico-chemical parameters, such as pH, BOD 5 , DO, dissolved ions and metals, etc., were used as dilution indicators to produce a Geo-referenced contamination plume for minero-medicinal spring water discharge. The pH is influenced by the dissolved species and various chemical reactions that differentially occur through the water column. The major reactions that affect the magnitude of pH are reactions that occur in aerobic/oxic conditions (Wetzel 1983;Morel and Hering 1993). Figure 4 shows the measured pH values increase from 7 to 7.2 from springs locations towards downstream, under oxidation reactions and are limited by reducing reactions (Stumm and Morgan 1981). A plume with a pH of 7.4 emerged in the confluence zone, which can be attributed to the mixing of water of the Euphrates River (pH range of 7.6-7.8) with that of Hijlan Creek (pH range of 7.0-7.2). A drop in pH is detected upstream (Fig. 5, pH). The DO dynamics of Hijlan Creek are not typical for a natural stream with storm runoff. The DO concentration range of 2-2.9 mg/l is attributed to the groundwater origin (oxygen consumption due to bacterial decomposition). Afterward, the gradual increase in DO concentration to 3.8 mg/l towards the confluence zone ( Fig. 4) which is due to the external contribution of oxygen from the solubilization of atmospheric oxygen. The rate of reaeration is assumed to be proportional to the difference between the saturation and observed concentrations of DO (mg/l). The reaeration rate coefficient K 2 (1/ time) is a sensitive parameter that can be calculated using the following Eq. (5) (Van Pagee 1978; Delvigne 1980): The onset of anoxic conditions is proximately followed by DO mixing zone (Fig. 5, DO), initiated by the water of Euphrates main body, which is defined as three eddies of DO plume ranging from 4.5 to 6.5 mg/L. At the end portion of the DO plume, Euphrates water was re-oxygenated by an aeration rate (k 2 ) of 0.51 (s −1 ) until the DO concentration reached 7.5 mg/l. The reverse phenomenon of BOD 5 concentration occurs in Hijlan Creek, as the concentration decreases from 5.5 to 1.8 mg/l towards the mixing zone (Fig. 4), due to air oxygenation in the direction of streamflow. This is followed by mixing-dilution in the Euphrates water of less than 1 mg/l of BOD 5 concentration (Fig. 5, BOD 5 ). Comparison of the measured BOD 5 values with the water quality standard indicates the water in the monitored zones is fair for the purposes of aquatic life but not recommended for drinking (Abdel- Reheem et al. 2019).
The observed concentration of nitrate (0.2-2 mg/l) in the zone of Hijlan inflow and Euphrates River is less than the permissible limit for drinking (Fig. 5, NO 3 ). No spatial mixing and dilution were detected because of alternative Redox reactions (water column oxygenation), bacterial nitrification to nitrate and/or denitrification to atmospheric as N 2 which is dependent on the amount of organic matter (Stumm and Morgan 1981). However, the phosphate concentrations were not measured at or above the detected analysis limit of 0.05 mg/l.

Self-purification factor
Dissolved oxygen deficit, saturated DO concentration, and concentration of DO (downstream) detected in DO plume (Fig. 5, DO) were used to investigate the self-purification factor depending on Eq. (2). Therefore, the deoxygenation coefficient and the reaeration coefficient must be calculated to obtain a self-purification factor as shown in Eqs. (6 ,7, and 8). 2.37 = 21 s. The model uses the coefficient k 1 , which is dependent on the contaminant characteristics while the re-aeration coefficient k 2 is dependent on water temperature, velocity, and depth of the river. The reaeration coefficient (k 2 ) value is 0.51 s −1 as previously calculated. From Eq. (6) (k 1 ) is: After integration, Eq. (6) (Waite and Freeman 1977;Kiely 1998;Omole and Longe 2012) gives: (f) = self-purification factor, which is defined by Eq. (8): The ability of the river water self-purification is a significant measure of river quality (Yilmaz et al. 2018;Elhag et al. 2019;Zubaidah et al. 2019). When the contaminants in the waterways are beyond the purification capacity of the river, they create significant pollution of the water system. The result of self-purification indicated that the Euphrates River has a good ability to purify the pollutants coming from the Hijlan springs due to the velocity in the water flow in the study area. In addition, the algae in the Euphrates River caused water to recover the rate of dissolved oxygen values that caused self-purification (Elhag et al. 2017).

Temperature and turbidity plume
Water temperature is frequently being used as a "tracer" to indicate the dilution and spatial distribution of other important water quality parameters that may occur within a mixing zone if the water temperature differential occurs. Domestic and/or wastewater is often warmer than the ambient environment. Therefore, thermal detection could be used to monitor the effects of sewage discharges on recreational areas. The water temperature of Hijlan Creek is 25.6 °C (hypothermal water), which decreases gradually to 24.6 °C with the flow direction (Fig. 4) as it is affected by air temperature (18 °C). Here and in the last 50 m of Hijlan valley, a mixed zone appears as shown in Fig. 6 (Temp). This zone was characterized by water temperature range of 22.6-24.6 °C, which is formed due to water mixing between Hijlan Creek (> 24.6 °C) and the main body of Euphrates River (< 22.2 °C). In the downstream direction, multi-temperature plumes of 24.6 °C are clearly observed near the right shoreline of the Euphrates River. The recovery zone of tepid water with a temperature of < 23.4 °C was detected in the last monitored water points. Turbidity is a water clarity measure that indicates the amount of debris in the water, which limits the passage of light. It is expressed by nephelometric unit (NTU). Light scattering turbidity measurements were taken at depths ranging from 10 to 35 cm. The lowest turbidity value of less than 0.7 NTU was recorded during low wind speed in the confluence zone, which gradually increased downstream reaching 1.02 NTU (Fig. 7, Tur). Comparison of the turbidity values with the water quality standard indicates the healthy limit for aquatic life. Normally, well-run municipal supplies have less than 0.5 NTU before disinfection and should be regulated to average 0.2 NTU or less.

Electrical conductivity (EC) and total dissolved solids (TDS) Plumes
The mixing of the Euphrates River with Hijlan Creek water, which possesses different electrical conductivities, can also exhibit TDS differentiation. The electrical conductivity values range from 2771 to 5076 µS/cm, while the TDS values vary between 2100 and 3640 mg/l, within a Hijlan stream (Fig. 4). Under a condition of dilution gradient of 11.2 µS/cm per meter and 10 mg/l per meter, the EC and TDS exhibit a range of 800-2700 µS/cm and 600-2100 mg/l, respectively (Fig. 6, EC and Fig. 7, TDS). The results show a direct relationship between the TDS plume and conductivity measures. Similar to conductivity, higher TDS concentrations were measured at the shoreline of the Euphrates River, where the shallow depth of the confluence zone causes water to mix vertically with rapid linear dilution. The confluence zone also exhibits full lateral dilution towards downstream sectors, depending on river bathymetry, water velocity, and discharge, to form the plume boundary interaction.
The total hardness is a measure of the calcium (Ca 2+ ) and magnesium (Mg 2+ ) content of water and is mainly used to assess the quality of water supply as an industrial water source. Variations in hardness reflect changes in dissolved water constituents, induced by water chemistry changes (Langmuir 1997). The water that flows from Hijlan Creek exhibits a higher hardness value (very hard water) than river water at the upstream site. A decrease in hardness concentration caused by discharge dilution was visibly observed at the site of mixing, indicated by the decline in TDS value from 1600 mg/l to 500-600 mg/l (Fig. 6, TH).
The mixing-dilution gradient of cationic water chemistry, such as K, Na, Mg and Ca within the beginning part of the contaminated plume was 0.8, 0.66, 0.83, and 0.5 ppm/meter respectively with an average of 0.69 ppm/meter (Fig. 7). The identified enrichment gradient relative to the river upstream in the mid and the tail of the plume reached 0.11, 1.06, 0.26, and 0.27 ppm/meter with an average of 0.43 ppm/meter. The difference between concentration dilution mechanisms in the onset of mixing, which is higher than the enrichment mechanism, is attributed to the water velocity and discharge differences, where the concentrations of the chemical ions are highly influenced by river flow dilution (Pasquini and Sacchi 2012).
The iso-concentration contour maps of the anionic water chemistry (Cl, SO 4, and HCO 3 ) (Fig. 7) closely follow the spatial distribution TDS content (positive relation) and pH values (an inverse relationship). This is likely due to alternate impacts of dilution and oxygenation mechanisms. The mixed water is slightly alkaline due to buffer bicarbonate (concentration range of 134-186 mg/l), caused by changes in water chemistry. Despite the low concentration of trace elements of copper and cadmium, their distribution is similar to that of dissolved ions, while no effect of spring water on the Euphrates was observed for manganese (Mn) and cobalt (Co). The changes in their concentrations are attributed to the conditions of river water movement and may be consistent with re-suspension of sediments from the bottom and solubilization of Mn and Co elements present in the sediment.

Contaminants loads and mixing mechanism
Euphrates has been subjected to chemical hazards contamination resulting from springs outflow. Thus, it is important to assess the degradation degree of the river and its effects of contamination on human health and fishery survival. The daily load discharge of contaminants to Euphrates was calculated using a standard flux-based algorithm according to the metrics of instantaneous discharge and concentration (Little  The daily loads of contaminants observed during the monitoring phase are listed in Table 4. The concentrations of anions and cations account for < 65 and 35% of the total contaminants, respectively, with very small percentages of heavy metals. The concentration of Cl − is used to calculate the mixing ratio because it is less affected by chemical reactions in the aqueous environment (Langmuir 1997). The rate of mixing of Hijlan Creek with Euphrates water in the confluence zone was calculated using the concentration of chloride ions (Mullaney et al. 2009), as shown in the following Eq. (10): where: R% signifies the proportion of chloride concentration between Euphrates River and Hijlan Springs, Cl downstream denotes chloride concentration of Euphrates water after the confluence zone, Cl upstream represents chloride concentration of Euphrates water before the confluence zone, and The results imply that 7.1% of Cl − in the confluence zone is derived from the Euphrates upstream and 92.9% comes from Hijlan Springs Creek with no storm runoff. The multisource water condition is attributed to enrichment caused by direct brackish disposal water. These percentile results were calculated under the following conditions: 1. Hijlan Creek water discharged into Euphrates River was 316,224 m 3 /day, with 420 and 1020 tons/day for chloride and TDS load discharge, respectively. 2. The upstream water discharge during the period of observation was 5.7 × 106 m 3 /day, with 867 and 3836 ton/day for Cl and TDS load discharge, respectively, R% = (230 mg∕l − 152 mg∕l) (1330 mg∕l − 230 mg∕l) × 100 = 7.1%. passes through the Euphrates River in the upstream sector. 3. The downstream discharge during the period of observation was 6.02 × 106 m 3 /day, with 1287 and 4856 tons/ day for Cl and TDS load discharge, respectively passes through the upstream river sector.

Natural water therapies and aquaculture
The subsurface litho-chemistry of the water-bearing horizons is a dominant factor that affects the chemistry of Hijlan springs water, where both dissolution and evaporation processes play a role in the enrichment of ions. Carbonate rocks (limestone, dolomitic limestone, and dolomite) of Ana and Euphrates Formations were partially dissolved, thus releasing Ca, Mg and HCO 3 into the aquifer. The high concentration of Na and Cl in the spring water is attributed to partial mixing of connate water with the meteoric water. Springs are resultant features of topography and crosscutting of the Abu Jir Fault Zone (Awadh and Abdul Al-Ghani 2013; Hussien et al. 2020a, b), where a set of aquifers are found along the fault planes. A Balneological water quality assessment was conducted according to the minero-medicinal Spa definitions (Jordana and Batista 2004), since the chemical properties of the spring water and its mixing with the Euphrates water can significantly affect human health. According to the results of Komatina (2004); Agishi and Ohatsuka (1998), a minero-medicinal water can be classified on the basis of total mineralization, ion concentrations and trace composition, acidity or alkalinity, and temperature. For Balneo-therapeutic assessment, some physicochemical parameters are compared with the well-known guidelines such as the European Union (2009) and US Spas (Lund 1996;Eaton 2004) (Table 5). Consequently, values of pH, TDS, TH, Ca 2+ , Mg 2+ , Na + , SO 4 2− , Cl − , HCO 3 − , NO 3 − , Pb, Zn, Fe, Mn, Cu, and Cd in the spring and the mixture of Hijlan Creek with the Euphrates waters are consistent with those of international Spas. Hence, the sampling water can be used for therapeutic purposes, beneficial for human well-being, and remedy for multiple diseases. The temperature of Hijlan water is described as being tepid to hypothermal (21.2-25.6 °C), which means it requires heating to be used as thermal water (38-44 °C) for therapeutic application (Matz et al. 2003). H 2 S measurements of water flowing from Hijlan springs indicate a small amount of H 2 S dissolved in water which appears at H1 and fades away at H5 (Table 2). These concentrations could be beneficial in the use of Creek Hijlan water as a balneological therapy. Generally, the water of Hijlan Creek is unsafe to drink due to the higher concentration of major cations and anions in comparison to the standard limits set by the World Health Organization (WHO 2011).
Hijlan Springs Creek was assessed for aquatic life purposes using the physicochemical parameters, such as temperature and existent metals (iron, nickel, copper, zinc, cadmium, and lead), as provided by Svobodova et al. (1993). The recommended guideline limit values for fish farming including the optimal pH range of 6.5-8.5 and a water temperature of approximately 15 °C. The tepid hypothermal water of Hijlan springs is unsuitable for aquaculture, given that its nitrate content (about 1 mg/l) is lower than the guideline limits, and the H 2 S concentration (1-2 mg/l) exceeds the guideline limit (0.002 mg/l). Based on the results, the Hijlan springs water appears unsuitable for fish farming. The toxic Fe content for fish cyprinid culture is accepted for concentrations less than 0.2 mg/l. Therefore, the water of Hijlan Creek is acceptable since it has a Fe concentration of zero (0). The water is also healthy in terms of the concentration of Ni, Cu, Zn, and Pb, except for Cadmium, which exceeds the guideline limit. Multiple therapeutic and restoration alternative uses of Hijlan Creek water may be recommended according to the plume behavior and character. For instance, through instream confluence management strategies, oxygenation of the mixing water can be increased, which improves aqua life habitat, reduces offensive odors, and improves water quality for water recreational value. Re-aeration strategies include natural water quality mixing-dilution mechanism, selective outflow distance, and flow routing improvement (weirs and barriers constructions in Hijlan Creek). Furthermore, artificial circulation by air diffuser may increase the re-aeration coefficient within the mixing plume but requires a minimum compressor size of flow rate. This modified design enables complete mixing of the water column and oxygenation for Balneo-therapeutic recreational value in swimming and restoration.
Oxygenation significantly increases available habitat for aqua life, while also lowering dissolved metal and nutrient concentrations, reducing odors, and possibly limiting algae growth. In shallow areas, settled fine particles are prone to re-suspension during periods of wave action, which can be mitigated by the use of Geobags or a sound rock breakwater.

Conclusions
This study focuses on an active hydrodynamic confluence zone with a water residence time of < 5 min, which is subjected to mixing of the water discharges of Hijlan Creek (316,224 m 3 /day) and Euphrates River (5.7 × 10 6 m 3 /day). A mass transport plume of minero-medicinal water was detected at a distance of 150 m from the mouth of the confluence, which acts as a single point source of 1020 tons/ day discharge for total dissolved load into receiving water. Although the base flow water of Hijlan Creek is classified as minero-medicinal water and can be used in water therapeutic purposes, the Creek water discharge is considered a point source of pollution, which adds different contaminants of up to 372,300 tons/year. The discharged load attenuated downstream due to mixing discharge rate of 5.5% from Hijlan Creek versus 94.5% from Euphrates River. Accordingly, the concentration dilution rate calculated from Cl − plume show that 92.9% of Cl − is derived from Hijlan Creek and 7.1% comes from the Euphrates upstream. The mixing-dilution processes within DO and BOD 5 plumes were generated in a condition of self-purification factor equal to 0.25, de-oxygenation coefficient (k 1 ) equals to 2.03 s −1 and re-aeration coefficient (k 2 ) equals to 0.51 s −1 .
Numerous physico-chemical plumes were detected, including plumes originating from the Creek collector springs. Water temperature and other important water quality variables are used as a "tracer" to define the dilution-enrichment boundaries and the spatial distribution of their concentration within the mixing zone. The mass transfer of the TDS concentration within the mixing TDS plume as represented by a dilution gradient reached 10 mg/l per meter with the flow direction. The chemical mixing occurred when parcels of Creek brackish water meet parcels of the Euphrates freshwater under different water velocity conditions, causing changes of ionic concentration. Neutral water of Hijlan Creek mixed with slightly alkaline water of the Euphrates River forming a plume of 7.4 pH in the confluence zone. It returns to its pH values as observed at the upstream site. Three anomalies of dissolved oxygen concentration plumes of 4.5-6.5 mg/l were observed at the same site of the temperature plume. At the end portion of DO plume the Euphrates water was oxygenated at the rate of 7.5 mg/l to create the opposite trend phenomenon of BOD 5 concentration then decreases downstream reaching 1.8 mg/l. The decreasing phenomenon in BOD 5 values is attributed to the external input of oxygen from the solubilization of atmospheric oxygen and discharge dilution mechanism, where most of the chemical ions and trace elements concentration are highly influenced by river flow dilution.